It is known practice to control the fuel injection of an internal combustion engine using an electronic control system which calculates and controls the flow rate of the various fuel injectors on the basis of the values taken by a certain number of operating parameters of the engine.
The information required for controlling the injectors includes the mass of cool air taken into the cylinders of the engine. This air mass directly determines the amount of fuel to be injected, the ratio of the air mass to the amount of fuel effectively being predefined for a given engine.
The mass of cool air taken into the cylinders of an internal combustion engine is however difficult to measure directly such that values of more accessible parameters which allow the approximately accurate value of this air mass to be recalculated on the basis of the laws of fluid mechanics and thermodynamics are conventionally used.
For example, patent EP 1 280 988 B1 which is incorporated by reference, provides a method for determining the air flow rate on the basis of the atmospheric pressure and the absolute pressure at the manifold measured in the intake manifold for a given crankshaft angle.
The accuracy of this method is entirely acceptable for four-stroke engines, but less so for two-stroke engines.
Specifically, it has been shown for two-stroke engines that a nonlinearity exists between the absolute pressure measured at the manifold and the engine load. The method according to patent EP 1 280 988 B1 therefore cannot be applied reliably for all of the loads to which a two-stroke engine may be subject. More specifically, in a two-stroke engine with a light load, the values of absolute pressure measured at the intake manifold are subject to substantial interference due to the combustion conditions which are more finely balanced than in a four-stroke engine.
It is known common practice to use an air flow meter to evaluate the mass of air delivered to a two-stroke engine. However, the use of a flow meter is too expensive a solution.